Population biology and invasion history of Puccinia striiformis f.sp. tritici at worldwide and local scale

Analyses of the large-scale population structure of pathogens enable the identification of migrationpatterns, diversity reservoirs or longevity of populations, the understanding of current evolutionarytrajectories and the anticipation of future ones. This is particularly important for long-distancemigrating fungal pathogens such as Puccinia striiformis f.sp. tritici (PST), which is capable of rapidspread to new regions and crop varieties. Although a range of recent PST invasions at continentalscales are well documented, the worldwide population subdivisions and the center of origin are stillunknown. In this study, we used multilocus microsatellite genotyping to infer the worldwidetel-00806507,version1-1Apr2013 Chapter I. Worldwide PST population structure and invasion history 22population structure of PST and the origin of new invasions based on 409 isolates representative ofthe distribution of the fungus on six continents. Bayesian and multivariate clustering methodspartitioned the set of multilocus genotypes into six distinct genetic groups associated with their likelygeographical origin. Analyses of the linkage disequilibrium and genotypic diversity indicated a strongregional heterogeneity in levels of recombination, with clear signatures of recombination in theHimalayan (Nepal and Pakistan) and near-Himalayan regions (China) and a predominant clonalpopulation structure in other regions. Our analysis confirmed the Middle East-Red Sea Area as themost likely source of newly spreading, high-temperature-adapted strains; Europe as the source of South American, North American and Australian populations; and Mediterranean-Central Asianpopulations as the origin of South African populations. The higher genotypic diversity, recombinantpopulation structure and high sex ability of the pathogen in the Himalayan region pinpoints this region as the possible center of origin of PST. Although most geographic populations are not markedlyaffected by recent dispersal events, this study emphasizes the importance of human activities on the recent long-distance spread of the disease.